Obesity is by definition an enlargement of the adipose depot. Thus, this proposal will examine critical variables which are known to influence the development of adipose tissue in man and other animals. We will focus on the contributions of insulin, glucagon, and exercise in the development of adipose cellularity and obesity. How do these variables effect, how are they affected by food intake and insulin resistance in muscle and adipose tissue? These factors will be examined in genetically obese mice and rats and in rats made obese by experimental diets. The objective of this proposal is to elucidate the sequence of events that result in the production and maintenance of obesity in several different animal models. In this way we can assess the relative importance of such variables in the etiology of obesity. The ultimate objective is to utilize the knowledge in prevention and treatment of human obesity.